Plant proteins, processed from cereal grains and legumes, are profitable ingredients in a wide variety of commercial food products, pet foods, and animal feed. Examples of the plant proteins that are currently available are soy protein concentrate, isolated soy protein, wheat gluten, rice, and corn proteins [Food Master (2003) Ingredients and R&D services catalog. Bensenville Ill. Business News Publishing Co. II. LLC].
However, plant proteins are often limiting in one or more essential amino acids. For example, the plant proteins of wheat, rice and corn are limiting in lysine [Hoseney, R C (1986) In: Principles of cereal science and technology. St. Paul, Minn.: American Association of Cereal Chemists, Inc. ppg. 69-88], whereas, soy protein is limiting in methionine and cystine [Haard and Chism (1996) In: Fennema Oreg., editor. Food Chemistry, 3rd ed. revised and expanded. New York: Marcel Dekker, ppg. 943-1011]. Though, well processed isolated soy proteins and soy protein concentrates have been found to be equivalent to animal protein in regard to the needs of human nutrition [Young, V R (1991) J. Am. Diet Assoc. 7: ppg. 828-835].
Yet, the following eight foods that are a good source of animal or plant protein account for 90% of all food allergenic reactions: soy, wheat, eggs, milk, peanut, treenut, fish and shellfish [Hefle, S. L. et al. (1996) Crit. Rev. Food Sci. Nutr. 36(5): ppg. 69-89]. Food allergens are a serious concern because essential nutrients for proper health can be missing with a narrowed food choice, in addition to the life-threatening concern of anaphylactic shock in highly sensitive individuals. Allergens are problematic for food producers because many food ingredients fall into this category and limit product development. The impact that food allergens, including undeclared food allergens, have had on the food industry is remarkable and the FDA has stated that food allergens are a top priority this year [Hefle, S. (Sep. 2003) Symposium: Update on Food Allergens. American Association of Cereal Chemists Annual Meeting. Portland, Oreg.].
As world food demands steadily increase, production of protein has to be maximized, as well as augmented. Plant proteins from cereals and legumes represent the main source of proteins and energy supply for both human and animal nutrition. This is partly due to the fact that animal proteins require much higher energy demand for production and are therefore more expensive to produce than plant proteins [Cheftel, J C et al. (1985) In: Fennema Oreg., editor. Food Chemistry, 2nd ed. New York: Marcel Dekker. ppg. 245-369]. For example, in order to produce 1 kg of animal protein, 3-20 kg of plant protein is needed. Consequently, as demands for animal protein increase globally, the need for plant protein increases drastically. To meet this need, new protein resources must be developed. Protein-rich crops that give equitable yields in underutilized growing regions are of paramount value for this purpose. Alternatively, new crops can be selected and tested for a protein source.
Since 1975, quinoa has become an alternative crop in North America and Europe for the following reasons [Fleming and Galwey (1995) In: Williams, J T, editor. Underutilized Crops: Cereals and Pseudocereals. New York: Chapman and Hall, ppg. 3-83]; quinoa has the ability to thrive in marginal soils, where traditional crops cannot, therefore, underutilized growing regions can be cultivated; quinoa has an average protein content of 14.6%, which is higher than traditional cereals, with certain varieties containing protein levels as high as 21.9%; and quinoa has an amino acid composition, protein efficiency ratio, protein digestibility, and nitrogen balance comparable to milk protein, casein. Consequently, it is rare for a plant protein to so closely resemble that of animal origin.
Quinoa protein is particularly high in lysine and methionine, amino acids limiting in cereal grains and legumes, respectively [Koziol, M J (1992) J. Food Composition and Analysis 5: ppg. 35-68]. Quinoa protein is also high in histidine, an essential amino acid for infant development and those with chronic diseases [Ettinger, S (2000) In: Mahan K L, Escott-Stump S, eds. Krause's Food, Nutrition, and Diet Therapy, 10th ed. Philadelphia, Pa. WB Saunders Co. ppg. 54-61]. In South America, it has been used as a weaning food for centuries because of its nutritional attributes and high protein digestibility.
Additionally, quinoa is not on the list of recognized food allergens. It is considered free of gluten or prolamins [Fairbanks, D J et al. (1990) Plant Breeding 104(3): ppg. 190-195], the protein associated with allergenic reactions in wheat gluten, rye and barley. Prolamins, like gliadins found in wheat, ignite immune responses in patients with gluten-induced enteropathy, also known as celiac disease. Quinoa is a pseudocereal named for its production of small grain-like seeds, although the actual harvested grain is a single seeded fruit [Shewry, P R (2002) In: Belton P S, Taylor J. eds. Pseudocereals and Less Common Cereals. Germany: Springer-Verlag Berlin Heidelberg. ppg. 93-122]. It is a dicotyledonous species not closely related to the monocotyledonous species of true cereal grains like wheat, rye, and barley. As a result of differences in plant taxonomy, quinoa does not contain the harmful amino acid sequences found in wheat. Therefore, it is concluded safe for a gluten-free diet [Thompson, T. (2001) J. Am. Diet. Assoc. 101: ppg. 586-587] and is recommended by the Celiac Disease Foundation and Gluten Intolerance Group. Furthermore, research presented at the International Workshop on Food Supplementation in Food Allergy and Immunity, found that quinoa is immunochemically safe and represents a viable alternative for gluten-free products [Berti, C et al. (Aug. 2002) International Workshop on Food Supplementation in Food Allergy and Immunity. Olsztyn].
Despite the numerous beneficial properties of quinoa as a plant protein source as described above, quinoa grain has not been processed efficiently to extract individual components contained therein. Currently, quinoa is available only as whole grain or ground for a small number of products. Therefore, there is a need in the art to develop a method to process quinoa grains into individual components, i.e., protein, oil, fiber, and starch, which are food-grade and/or pharmaceutical-grade that can readily be utilized as nutritional supplements as well as agents for providing functionality in a variety of food products, cosmetic products, and animal feeds. The present invention meets this need. The advantage of the invention will be evident in the following description.